1. Field of the Invention
The present invention relates to a filling liquid for distribution, which is to fill a nozzle flow path communicating with an ink discharge port during distribution of a thermal ink jet recording head (ink jet head), to an ink jet head using the filling liquid for distribution, and to a distribution method for the ink jet head.
2. Description of the Related Art
Hitherto, as a thermal ink jet head, there has been known an ink jet head having a structure in which a plurality of nozzle flow paths partitioned by nozzle walls are formed, a plurality of ink discharge ports communicating with the nozzle flow paths are formed, and a heater is disposed in each nozzle flow path. The ink jet head having the above-mentioned structure has a mechanism in which ink filling the inside of each nozzle flow path is heated by a heater to make the ink bubble (foam) to fly liquid droplets of ink from the ink discharge ports.
The ink jet head having the above-mentioned structure has a problem in that, when ink for printing is conserved while filling the nozzle flow paths for a long period of time, the ink is thickened or solidified owing to the volatilization of an ink solvent, and the discharge performance of the ink jet head is degraded even when the ink jet head is subjected to a recovery operation. In a piezoelectric system in which mechanical deformation of a piezoelectric element makes droplets of ink fly, even when ink is thickened or solidified, an ink jet head can be recovered by a recovery operation in most cases. On the other hand, in a thermal system in which heating of a heater makes droplets of ink fly, the above-mentioned problem becomes more serious. Conversely, when the ink jet head is conserved for a long period of time while the nozzle flow paths are kept empty, the surface of the heater is exposed to outside air to be contaminated, and the discharge performance of the ink jet head is degraded during printing, which may degrade printing quality.
Considering the above-mentioned problem, it has been proposed to fill the inside of a recording head with only ink for conservation instead of ink for printing during conservation or distribution before start of use (Japanese Patent Application Laid-Open No. H05-169676). Japanese Patent Application Laid-Open No. H05-169676 proposes that a liquid containing water and diethylene glycol as constituents, ink subjected to deaeration, or the like be used as the ink for conservation. It has been also proposed that a flow path of an ink jet head be filled with a conservation liquid containing a humectant, a nonionic surfactant, and a dye during shipment, transport, and conservation of a printer (Japanese Patent Application Laid-Open No. 2000-168056). Japanese Patent Application Laid-Open No. 2000-168056 proposes that a water-soluble organic solvent having a plurality of hydroxyl groups, in particular, one having a viscosity of less than 40 centipoises be used as the humectant.
Further, it has been known that, in the thermal ink jet head, the surface state of the periphery of an ink discharge port greatly influences ink dischargeability (discharge performance of the ink jet head) owing to the mechanism of allowing ink to fly with heat energy. Specifically, the thermal ink jet head has a problem in that discharged ink gets around an outer surface (also referred to as “face surface”) of the ink discharge port depending on the surface state of the periphery of the ink discharge port, with the result that a liquid pool is formed on the periphery of the discharge port. The liquid pool is not preferred because it causes ink to fly in a direction displaced from a direction (normal direction) in which the ink is supposed to fly and leads to the occurrence of so-called “misdirection print” and the degradation in printing quality.
In view of the foregoing, it has been proposed to form a hydrophilic region in a peripheral area of a discharge port on the face surface in a recording head for aqueous pigment ink (Japanese Patent Application Laid-Open No. 11-334074). Japanese Patent Application Laid-Open No. 11-334074 proposes that a hydrophilic region be formed by, for example, surface roughening by laser irradiation or the like, or formation of a hydrophilic film made of a water-soluble resin such as hydroxypropyl cellulose, etc.
It has also been proposed to form a water-repellent region in a peripheral area of a discharge port on the face surface in a recording head for aqueous pigment ink (Japanese Patent Application Laid-Open No. H11-334074). Japanese Patent Application Laid-Open No. H11-334074 proposes that a water-repellent region be formed by, for example, coating with a water repellent agent.
The ink for conservation described in Japanese Patent Application Laid-Open No. H05-169676 and the conservation liquid described in Japanese Patent Application Laid-Open No. 2000-168056 exhibit certain effects of preventing the solidification of ink caused by long-term conservation and the contamination of a heater to keep the discharge performance of an ink jet head and printing quality, but have the following problems.
In recent years, in an ink jet printer, there has been a demand for miniaturizing pixels so as to perform printing with high precision and high resolution (for example, the amount of one droplet of ink is 10 pL or less), and the size of an ink discharge port of an ink jet head has been being reduced. Even when the ink for conservation described in Japanese Patent Application Laid-Open No. H05-169676 and the conservation liquid described in Japanese Patent Application Laid-Open No. 2000-168056 are applied to the ink jet head having an ink discharge port with a small aperture formed therein, the effect of preventing the thickening and solidification of ink caused by long-term conservation and the contamination of a heater so as to keep the discharge performance of an ink jet head and printing quality cannot be obtained sufficiently.
There is also a problem in that, when the ink for conservation described in Japanese Patent Application Laid-Open No. H05-169676 and the conservation liquid described in Japanese Patent Application Laid-Open No. 2000-168056 are applied to the recording head having a hydrophilic region formed therein as described in Japanese Patent Application Laid-Open No. H11-334074, the surface state of the hydrophilic region changes and the hydrophilicity thereof is degraded. This is not preferred because the discharge performance is not obtained as originally expected in spite of the fact that the hydrophilic region is formed on a discharge port formation surface, and “misdirection print” and degradation in printing quality occur.
There is also a problem in that, when the ink for conservation described in Japanese Patent Application Laid-Open No. H05-169676 and the conservation liquid described in Japanese Patent Application Laid-Open No. 2000-168056 are applied to the recording head having a water-repellent region formed therein as described in Japanese Patent Application Laid-Open No. H11-334074, the surface state of the water-repellent region changes and the water repellency thereof is degraded. This is not preferred because the discharge performance is not obtained as originally expected in spite of the fact that the water-repellent region is formed on a discharge port formation surface, and “misdirection print” and degradation in printing quality occur.